The invention relates to a device for blow moulding containers of a thermoplastic material that has at least one blow station with at least one blow mould that is comprised of at least two blow mould segments held by supports and wherein at least one of the blow mould segments is arranged such that it can slide relative to its support.
In this type of container moulding using blow pressure action, preforms of a thermoplastic material, for example preforms of PET (polyethylene terephthalate), are delivered to different processing stations within a blow moulding machine. Typically, such a blow moulding machine has a heater unit and a blow unit in which the previously temperature treated preform is expanded by biaxial orientation to a container. The expansion is accomplished with the use of compressed air, which is introduced into the preform to be expanded. The process sequence of such an expansion is explained in DE-OS 43 40 291.
The basic structure of a blow station for moulding containers is described in DE-OS 42 12 583. Options for temperature treatment of the preforms are explained in DE-OS 23 52 926.
Within the device for blow moulding, the preforms and the blow-moulded containers can be transported by means of various handling devices. One proven technique in particular is the use of transport mandrels onto which the preforms are placed. The preforms can also be handled with other carrying devices, however. For example, the use of grippers for handling preforms, and the use of expansion mandrels that can be introduced into a mouth area of the preform are also among the available designs.
The aforementioned handling of the preforms takes place on the one hand as part of the so-called two-stage process, in which the preforms are first manufactured in an injection moulding process, then are stored temporarily, before later being conditioned with respect to their temperature and blow moulded into containers. On the other hand, application is also found in the so-called one-stage process, in which the preforms are appropriately temperature treated and then blow moulded immediately after their production by injection moulding and adequate hardening.
As regards the blow stations employed, various different embodiments are known. In blow stations that are arranged on rotating transport wheels, one frequently encounters mould supports that swing open in a book-like fashion. However, it is also possible to use mould supports that slide relative to one another or operate in other ways. In stationary blow stations, which are especially suitable for accommodating multiple cavities for container moulding, plates that typically are arranged parallel to one another are used as moulds.
Typically, devices for processing thermoplastics use moulds that must be suitably temperature treated to ensure short process cycles. Often, it is not only temperature treatment to a predetermined temperature level that is performed; instead the mould is first heated as a function of the relevant process steps and is cooled after insertion or moulding of the thermoplastic is completed in order to attain dimensional stability of the plastic item as quickly as possible.
Oils or water are typically used as temperature control media. These liquid temperature control media flow through the parts requiring temperature treatment in the area of coolant channels. Heat transfer is accomplished through contact of the temperature control medium with the wall of the coolant channel. The efficiency of the heat transfer in each case is dependent upon the temperature difference between the temperature of the channel wall and the temperature of the temperature control medium in a vicinity of the wall.
During design of the blow stations, different requirements must be met, where each optimization made with respect to only a single requirement can be expected to have negative effects with regard to the other requirements. On the one hand, for example, the lowest possible structural weight is desired, but on the other hand adequate structural strength must be provided on account of the exposure to high internal pressure. Likewise, it is necessary to ensure that the mould parts are pressed together sufficiently strongly despite the internal pressure action so as to avoid formation of a gap that would result in a discernible seam in the exterior region of the blow-moulded containers.
Consequently, the object of the present invention is to design a device of the aforementioned type that has a low structural weight while achieving convenient guiding of the blow mould segment that can slide relative to its support.
This object is attained in accordance with the invention in that the support is equipped with at least two guide elements for the movable blow mould segment and in that the guide segment has a hard core that is connected to the blow mould segment and that is embedded, at least in part, in an elastomer that is carried by the support.
Another object of the present invention is to design a seal such that a strong sealing effect is achieved, in order to bolster pneumatic bracing of the movable blow mould segment relative to its support.
This object is attained in accordance with the invention in that the blow mould segment is sealed by a circumferential elastomer seal with respect to the support in an area of action provided for the application of pneumatic pressure, and in that the seal has a seal lip that makes area contact with the support when pressure is applied.
Due to the use of a guide element with a hard core that is embedded in an elastomer, it is possible to support the blow mould segment in a manner similar to the use of a stud guide and simultaneously to use the flexible properties of the elastomer to compensate for manufacturing tolerances. In addition, in the event of a deflection of the blow mould segment, the elastomer provides restoring forces that cause an elastic return to the initial position once application of the pneumatic pressure stops.
The design of the seal with a seal lip that makes area contact with the support provides a very strong sealing effect, thus avoiding loss of pressure. As compared to seals in the form of O-rings, which provide a merely linear contact surface, the use of the area contact seal lip provides a greatly increased sealing effect, and thus offers significantly superior efficiency.
A direct connection between the core and the blow mould segment can be accomplished in that sections of the core protrude out of the elastomer.
The use of universal components can be supported in that the core is connected to the blow mould segment by a coupling element.
A compact configuration is supported in that the combination of the core and the elastomer is designed in the manner of a sleeve.
To achieve economical manufacture of the necessary recesses for holding the components, it is proposed that the elastomer surrounds the core with a rounded shape.
The number of components used can be reduced in that the core is directly connected to one mould part.
In order to support manufacture of product-specific mould parts that are light in weight and are easily interchangeable, it is proposed that the core is connected to an intermediate shell that supports the mould part.
Delivery of preforms and discharge of blow-moulded containers is facilitated in that the supports are hinge-jointed to one another.
An easily implemented preloading can be achieved in that provision is made for the application of pressure to determine positioning of the movable blow mould segment.
To ensure that the mould parts abut one another even when internal pressure is applied during container moulding, it is proposed that one of the mould parts can be pneumatically braced with respect to the other mould part.
To accomplish a high degree of efficiency in generating preloading, it is proposed that at least one of the mould parts is held in place so as to be sealed with respect to the support.
Further simplification of the configuration can be accomplished in that, in order to provide a preloading force, provision is made for an area of pressure action that is delimited by a circumferential seal.
To ensure a high-quality pressure seal with minimal device complexity, provision is made for the guide elements to be arranged outside the area of pressure action.
Large-area contact of the seal lip during the application of pressure is supported in that the seal lip has a base block that is connected by a tapered part to a seal lip, sections of which lip extend a distance from a base projection of the base block and, in combination with the base projection, delimits a seal notch.
In particular, in order to achieve intended deformation of the seal, it is useful for the seal notch to be arranged to face an area of pressure action.